The actors who provide the voice-overs for video game characters are considering striking over pay and conditions.

Some voice-overs, for games such as Call of Duty, lead to "vocally stressful sessions" for actors

The union that represents them wants better protection and pay for roles that cause "voice stress" such as repeated shouting.

It also wants a clearer definition between the roles of voice actors and those who are involved in motion capture.

Members are due to vote next month.

The Screen Actors Guild - American Federation of Television and Radio Artists (Sag-Afrta) said that, if more 75% of members agree, then all union members working on video games will go on strike.

It wants actors to get stunt pay for vocally stressful recording sessions and for such sessions to be restricted to two hours.

It is also calling for performance bonuses each time a game sells two million copies.

Actors contribute to the success of a game, argues the union

The strike has been supported by some prominent actors who have united on Twitter via the hashtag #PerformanceMatters.

In a blogpost, Wil Wheaton, who provided voice-overs for Grand Theft Auto, explained why he is supporting the strike.

"I fully realise that for anyone who doesn't work as a voice actor it sounds insane to care about vocally stressful sessions," he said.

He invited critics to "grab your favourite book" and read aloud from it for several hours.

"If you've done this as I asked, it's now six or seven hours after you started. Don't talk at all for the rest of the day and don't make any plans to go audition for any other voice work for the rest of the week, because your voice is wrecked."

The union also wants actors to be given more information about the roles that they are auditioning for. It called for stunt co-ordinators to be on set when actors do motion capture work - something which voice actors are increasingly being asked to do.

"Asking us to go into something with absolutely zero knowledge about the project, or what we'll be expected to do if we are cast, is completely unreasonable," said Mr Wheaton.

"Maybe someone has a moral objection to the content of a game, and they'd like to know what it is before they commit to it."